The Vagabond Family of new aircraft
|The Etruria E200 Vagabond
The Etruria E200TC Vagabond
|An aircraft with the Three Lifting
Surface Configuration (3LSCTM) is configured with a canard wing
mounted in the forward section of the fuselage in front of the main
wing, a main wing and a horizontal tail installed in the traditional
location, behind the main wing.
Major advantages of the 3LSCTM derive from the added flexibility in selecting the aircraft geometry with regard to the payload-wing-fuselage relative position, and compliance with control & stability requirements over an extended c.g. range under all certified flight conditions.
The 3LSCTM also permits an unobstructed passenger cabin to be positioned in front of an aerodynamically superior mid-fuselage wing position, provides for landing gear retraction into the aft fuselage body without external protrusions, and allows the engine to be in pusher configuration far behind the passengers. This leads to a significant reduction of aircraft cross-section area and consequent reduction of aerodynamic drag, especially in general aviation and commuter aircraft.
The other significant advantage of the 3LSCTM is the dramatic reduction of the total lifting area required to fly the aircraft. This leads to a consequent reduction of total wetted area and aerodynamic drag. It is well known that the canard + wing configuration is potentially capable of offering better aerodynamic efficiency than the wing + tail configuration. This derives from the fact that the rotation of the aircraft at take-off, or approaching the landing speed, is obtained by applying upward aerodynamic forces on the front surface instead of down loads on the conventional tail, so a lesser lifting surface is required to balance the aircraft weight. Small and commercial aircraft have the lifting area determined by the minimum speed requirements for these two flight conditions. As a consequence, when flying at cruise speed, they have a total lifting surface exceeding the minimum required for cruise flight. Considering that these aircraft spend the greatest part of flight time at cruise, the negative impact of this additional wing area on the aerodynamic efficiency is very significant.
Theoretically, the pure canard (two-lifting surface) configuration shows the possibility of reducing the total wing area of the aircraft, but, in the real world, this is spoiled by a number of problems typical of pure canard aircraft. In contrast to a horizontal tail in the traditional location behind the wing, a lifting surface in front of the wing has a destabilizing effect and therefore cannot both be large enough to balance all pitching moments generated by the c.g. excursion and, at the same time, small enough to comply with the stability requirements. The result is that the pure canard configuration cannot optimize both the control and stability characteristics and maintain a satisfactory c.g. range under all flight conditions.
Another adverse effect for the canard aircraft is determined by the flap extension, because of the large variation of pitching moment produced by this operation. All of the pure canard aircraft have a very limited c.g. range and no flaps, or flaps with minimum effect. The effect of reducing the flap is that it requires a larger lifting surface area to maintain the same minimum speed, thus reducing the advantage of the canard configuration unless an artificial stability augmenter system is installed, but this is not appropriate for small aircraft. The other challenging possibility is to add a small horizontal surface behind the wing to compensate for the reduction of the aircraft stability due to the presence of a canard surface large enough to assure the required controllability of the aircraft in every flight condition and c.g. position.
Analysis and tests demonstrate that a well-optimized 3LSCTM may offer exceptional efficiencies. The Piaggio P180 Avanti, a twin-engine executive aircraft designed to exploit all benefits of the 3LSCTM, is proving with its daily flight operations, dramatic flight performance, not achieved by the contemporary traditional aircraft.